/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.jn.langx.escape;

import com.jn.langx.util.Preconditions;

import java.util.Map;

/**
 * A {@link CharEscaper} that uses an array to quickly look up replacement characters for a given
 * {@code char} value. An additional safe range is provided that determines whether {@code char}
 * values without specific replacements are to be considered safe and left unescaped or should be
 * escaped in a general way.
 * <p>
 * <p>A good example of usage of this class is for Java source code escaping where the replacement
 * array contains information about special ASCII characters such as {@code \\t} and {@code \\n}
 * while {@link #escapeUnsafe} is overridden to handle general escaping of the form {@code \\uxxxx}.
 * <p>
 * <p>The size of the data structure used by {@link ArrayBasedCharEscaper} is proportional to the
 * highest valued character that requires escaping. For example a replacement map containing the
 * single character '{@code \}{@code u1000}' will require approximately 16K of memory. If you need
 * to create multiple escaper instances that have the same character replacement mapping consider
 * using {@link ArrayBasedEscaperMap}.
 */
public abstract class ArrayBasedCharEscaper extends CharEscaper {
    /**
     * The replacement array (see ArrayBasedEscaperMap).
     */
    private final char[][] replacements;
    /**
     * The number of elements in the replacement array.
     */
    private final int replacementsLength;
    /**
     * The first character in the safe range.
     */
    private final char safeMin;
    /**
     * The last character in the safe range.
     */
    private final char safeMax;

    /**
     * Creates a new ArrayBasedCharEscaper instance with the given replacement map and specified safe
     * range. If {@code safeMax < safeMin} then no characters are considered safe.
     * <p>
     * <p>If a character has no mapped replacement then it is checked against the safe range. If it
     * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed.
     *
     * @param replacementMap a map of characters to their escaped representations
     * @param safeMin        the lowest character value in the safe range
     * @param safeMax        the highest character value in the safe range
     */
    protected ArrayBasedCharEscaper(
            Map<Character, String> replacementMap, char safeMin, char safeMax) {

        this(ArrayBasedEscaperMap.create(replacementMap), safeMin, safeMax);
    }

    /**
     * Creates a new ArrayBasedCharEscaper instance with the given replacement map and specified safe
     * range. If {@code safeMax < safeMin} then no characters are considered safe. This initializer is
     * useful when explicit instances of ArrayBasedEscaperMap are used to allow the sharing of large
     * replacement mappings.
     * <p>
     * <p>If a character has no mapped replacement then it is checked against the safe range. If it
     * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed.
     *
     * @param escaperMap the mapping of characters to be escaped
     * @param safeMin    the lowest character value in the safe range
     * @param safeMax    the highest character value in the safe range
     */
    protected ArrayBasedCharEscaper(ArrayBasedEscaperMap escaperMap, char safeMin, char safeMax) {
// GWT specific check (do not optimize)
        Preconditions.checkNotNull(escaperMap);
        this.replacements = escaperMap.getReplacementArray();
        this.replacementsLength = replacements.length;
        if (safeMax < safeMin) {
            // If the safe range is empty, set the range limits to opposite extremes
            // to ensure the first test of either value will (almost certainly) fail.
            safeMax = Character.MIN_VALUE;
            safeMin = Character.MAX_VALUE;
        }
        this.safeMin = safeMin;
        this.safeMax = safeMax;
    }

    /**
     * This is overridden to improve performance. Rough benchmarking shows that this almost doubles
     * the speed when processing strings that do not require any escaping.
     */
    @Override
    public final String escape(String s) {
        // GWT specific check (do not optimize).
        Preconditions.checkNotNull(s);
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if ((c < replacementsLength && replacements[c] != null) || c > safeMax || c < safeMin) {
                return escapeSlow(s, i);
            }
        }
        return s;
    }

    /**
     * Escapes a single character using the replacement array and safe range values. If the given
     * character does not have an explicit replacement and lies outside the safe range then {@link
     * #escapeUnsafe} is called.
     */
    @Override
    protected final char[] escape(char c) {
        if (c < replacementsLength) {
            char[] chars = replacements[c];
            if (chars != null) {
                return chars;
            }
        }
        if (c >= safeMin && c <= safeMax) {
            return null;
        }
        return escapeUnsafe(c);
    }

    /**
     * Escapes a {@code char} value that has no direct explicit value in the replacement array and
     * lies outside the stated safe range. Subclasses should override this method to provide
     * generalized escaping for characters.
     * <p>
     * <p>Note that arrays returned by this method must not be modified once they have been returned.
     * However it is acceptable to return the same array multiple times (even for different input
     * characters).
     *
     * @param c the character to escape
     * @return the replacement characters, or {@code null} if no escaping was required
     * <p>
     * // will do: Rename this something better once refactoring done
     */

    protected abstract char[] escapeUnsafe(char c);
}
